Outdoor navigation has been widely deployed, given the development of various global-navigation-satellite-systems (GNSS). However, such navigation systems do not work well for indoor applications, as indoor environments do not facilitate the effective reception of signals from GNSS satellites.
Indoor navigation systems have been recently developed that are based on wireless networks, such as, for example, Wi-Fi. However, such networks are specifically designed and used for wireless communications and not necessarily optimized for navigation or positioning. Indeed, various attempts have been made to develop indoor navigation systems using time-of-flight (ToF) methods. Time-of-flight (ToF) is basically the overall time that a signal propagates from a wireless device to a network access point (AP) and back to the wireless device. This time value can be converted into distance using the speed of light. ToF methods are considered robust and scalable, but require hardware changes to WiFi modem. ToF methods also generally pose a high barrier-to-entry, since implementation requires substantive changes in current navigation and wireless technologies.